Host-parasite dynamics set the ecological theatre for the evolution of state- and context-dependent dispersal in hosts

Abstract

While host-parasite interactions are ubiquitous, the large scale consequences of parasite infections are mainly driven by the spatial context. One trait of pivotal importance for the eco-evolutionary dynamics of such metapopulations is the spatial behaviour of hosts, that is, their dispersal. It is well established that dispersal is not a random process, rather dispersal is informed and may depend on internal and external factors. In host-parasite metapopulations, dispersal may be a function of a host’s infection state, but also of the local context, such as host density or parasite prevalence. Using a dynamical host-parasite metapopulation model, we explore whether host dispersal evolves to be state- and context-dependent and what shapes the evolutionarily stable dispersal reaction norms have. We show that state-dependent dispersal readily evolves in the sense that hosts disperse more when infected. This dispersal bias evolves due to kin selection which is consistent with previous studies. Most importantly, we show that prevalence-dependent dispersal evolves, especially when virulence is high and epidemiological dynamics have predictable signatures. The observed evolutionary outcome, a negatively prevalence-dependent dispersal reaction norm for susceptible hosts, seems counter-intuitive at first. However, our results can be readily explained by the emergent epidemiological dynamics, especially their spatial and temporal correlation patterns. Finally, we show that context-dependency in dispersal may rely on both, prevalence, but also host density cues. Our work provides new insights into the evolution of complex dispersal phenotypes in host-parasite metapopulations as well as on associated feedbacks between ecological dynamics and evolutionary change.

Parasitism and host dispersal plasticity in an aquatic model system

“…In this way, the prey can take the appropriate "decision" to leave or stay in the patch. This condition is also found in a model considering host-parasite context-dependent plasticity (Deshpande et al, 2020). A recent study analysing multiple taxa of invertebrates and vertebrates showed that chemical predator-related cues can induce dispersal, along with alterations in resource availability (Fronhofer et al, 2018).…”

“…x infection prevalence interaction would indicate genetic variation in this plasticity. Finally, we also added population density as a covariate to take into account this potential additional type of context-dependency (Fellous et al, 2012;Deshpande et al, 2020), and we considered experimental block as random factor. We excluded 11 replicates from the state-and context-dependent analysis because no infection was detected.…”

“…The theoretical model of Deshpande et al (2020), predicts that positive parasite induced state-dependent dispersal can evolve as a consequence of kin selection. Dispersal of infected individuals is promoted to prevent relatives to be affected.…”

“…This highlight the presence of a genetic basis for context-depend dispersal. Theoretical models (Deshpande et al, 2020;Poethke et al, 2010) predict that, for the prey or parasite to make the appropriate "dispersal decision"…”

“…Kin selection can also be a major driver in increasing dispersal. Individuals may leave their patch to prevent relatives to be infected, even if dispersal is not favoured by other conditions (Hamilton & May, 1977;Poethke et al, 2010;Iritani & Iwasa, 2014;Iritani, 2015;Deshpande et al, 2020). In other cases, parasites do not seem to affect dispersal behaviour of their hosts (Mayer et al, 2015;Nelson et al, 2015;Csata et al, 2017;Taggart et al, 2018).…”